This invention relates to a mechanism for operating a metering valve comprising two rotary registers shaped as spherical or cylindrical domes and provided with cutouts which are symmetrical in relation to the axis of a central opening defined by the movement of the registers and cutouts. The registers are fastened to two drive shafts disposed coaxially in relation to one another and received in the bearings of a flow tube. By pivoting about their common axis, each of the registers are operated synchronously and in opposite directions. Each of the two shafts is provided with an arm, each arm being articulated by means of a connecting rod on a rocking lever mounted on a pivot axis parallel to the common axis of the two shafts. The rocking levers are connected to drive device pivoting them about their pivot axis. The articulation between one of the rocking levers and its connecting rod is angularly offset about the pivot axis in relation to the articulation between the other rocking lever and its connecting rod.
A mechanism of the type contemplated by the present invention is described in European Pat. No. 0,134,918, corresponding to U.S. Pat. No. 4,570,900, assigned to the assignee hereof, all of the contents of which are incorporated herein by reference. U.S. Pat. No. 4,570,900 discloses an apparatus for regulating the flow of charge material from a storage container disposed on the central axis of a shaft furnace charging plant. This prior device discloses means for controlling the registers in such a manner that the flow opening delimited by the cutout, will be modified symmetrically in relation to the central axis.
The use of the metering system of U.S. Pat. No. 4,570,900 results in a certain irregularlity in the level of the charging surface of the furnace. This irregularity has, in addition, been confirmed by tests. The tests have shown that these irregularities are due to the offsetting (in relation to the vertical axis), of the flow of charge material flowing through a symmetrical opening defined between the two registers. It is true that this offset is very slight and that its effect on the charging profile varies in accordance with the angular position of the spout. However, since the same effects always occur in the same angular positions (viewed in plan) of the spout, the accumulation of these irregularities as successive deposited layers finally gives rise to a non-negligible deviation from the charge level profile which it is desired to obtain.
It has been found that the cause of this offset of the flow current is due to the difference in the curvature of the domes of the two registers, one of which must have a radius greater than that of the other. It will be appreciated that this offsetting phenomenon will be better understood and described in greater detail further on, in connection with the drawings.